LETTERS Anomalous Dispersion of Chemical Waves in a Homogeneously Catalyzed Reaction System

We present experimental results that demonstrate anomalous dispersion in a Belousov-Zhabotinsky system. The reaction is carried out at high concentrations of sulfuric acid and involves 1,4-cyclohexanedione as its organic substrate. The unusual dispersion behavior of this excitable medium induces an attractive interaction between pulses that results in fusion or closed stacking of waves. Experimental results from quasi-one-dimensional as well as two-dimensional media are presented. In two-dimensional reaction systems, a complex dependence of the propagation velocity on the relative direction between fronts is found and the formation of spiral defects is observed. Propagating waves of excitation have been observed in a variety of chemical and biological reaction-diffusion systems such as the Belousov-Zhabotinsky (BZ) reaction,1 the oxidation of CO on Pt surfaces,2 aggregating slime molds,3 yeast extracts,4 and cardiac tissue.5 Excitation waves have typically constant profiles and propagation velocities. The propagation velocity of wave trains, however, shows a pronounced dependence on the distance between the pulses (i.e., the wavelength of the wav